CHICAGO — For nearly 30 years, Scabby the Rat, a giant inflatable balloon with sharp claws, a snarl and a menacing demeanor, has loomed over construction sites across Chicago and beyond to protest the hiring of nonunion labor.

Like deep dish pizza, skyscrapers and the Ferris Wheel, the giant inflatable rat is a Chicago creation that has found its way into the broader culture. Scabby had a memorable star turn on a “Sopranos” TV episode centered around a construction work stoppage.

But soon, Scabby the Rat — who comes in a variety of sizes and designs — may be out of work.

The National Labor Relations Board previously gave the giant rats a wide berth, but it’s shifted its stance under the Trump administration. The board is weighing whether to crack down on their use, on the grounds that the rats may be scaring away customers from “neutral” businesses not involved in the labor dispute.

“Their use is unlawful under the (National Labor Relations) Act and not protected under the First Amendment because they are being used specifically to menace, intimidate and coerce in aid of an unlawful purpose,” Peter Robb, the NLRB’s general counsel, said in a brief filed last month.

Banning the rats not only would eliminate what has become the go-to protest symbol for many local unions, but it would also be a blow to Big Sky Balloons, a company in southwest suburban Plainfield, Illinois, that created and manufactures Scabby.

Scabby was commissioned in 1990 by the bricklayers union in Chicago, which was looking for an eye-catching way to make its case against alleged unfair hiring practices. A protest icon was born, and rats as tall as 25 feet have been inflated at construction sites on behalf of a variety of trade unions ever since.

“Everybody in Chicago knows what the rat is and that somebody is on strike,” said James Allen, president of District Council 1 of the International Union of Bricklayers in Elmhurst, Illinois.

Use of the rat over three days last summer by the International Brotherhood of Electrical Workers in Philadelphia is facing a stiff test before the National Labor Relations Board.

Protesting the hiring of nonunion labor during the renovation of a downtown Fairfield Inn, the local union brought in two 8- to 12-foot rats, positioning them between the entrances to the hotel and restaurant and scaring away customers, according to a complaint filed by the hotel with the NLRB.

The five-member board has yet to rule on the complaint, but the brief filed by Robb, the agency’s general counsel, didn’t mince words.

“A huge, menacing inflatable rat placed near a business entrance thus inherently conveys a threatening and coercive message that will restrain a person,” the brief stated. “For three days, pedestrians, guests, employees and contractors could not avoid large, intimidating, hostile-looking inflatable rats that were mere feet, and sometimes inches, away from them.”

There is no disputing that the rat balloons were meant to be threatening.

Mike and Peggy O’Connor launched Big Sky Balloons in Plainfield as a hot air balloon ride company in 1980.

The couple moved into advertising a few years later, inflating large tethered balloons above car dealers and store grand openings. The business really took off in 1990, when they created Scabby for the local Bricklayers union.

“They called him with the idea; Mike came up with the design,” Peggy O’Connor said. “The guy said he wanted it meaner looking, with festering nipples and big claws. Mike redesigned it and the guy liked it.”

Rats range in size from 6 feet to 25 feet, and in price from about $2,600 to $9,300 each, she said. Big Sky sells about two to three Scabby the Rat balloons a month.

In addition to Scabby, Big Sky sells other inflatable vermin, including “Cockroach,” “Fat Cat” and “Greedy Pig,” all of which may be endangered by the pending NLRB case.